The field of the present invention relates to data reading systems. In particular, an optical scanning and method for optical scanning are described herein for creating for creating a dense scan pattern with potentially a wide range of reading distances.
Longer range scanners have been proposed of a variety configurations. In U.S. Pat. No. 5,869,827 (Rando), multiple beam sources and distance sensing mechanisms are employed to provide an extended focus range. U.S. Pat. No. 5,641,958 (Rudeen et al.) discloses a system as employed in the PSC SP400LR scanner in which an LCD diffractive control module changes the waist location of the scanning beam. In U.S. Pat. No. 4,560,862 (Eastman et al.) the facets of a polygon mirror are provided with different curvatures such that the scan lines produced by the different facets are focused at varying distances. U.S. Pat. No. 5,475,207 (Bobba, Acosta et al.) discloses a variety of single and multiple source laser scanners, and single and multiple scan mechanisms for creating relatively dense scan patterns through multiple scan housing windows.
Typical scanners rely on the number of facets in the polygon mirror and the number of pattern mirrors to generate a certain number of scanning segments or scan lines. The number of pattern mirrors is limited by the size of the scanner housing.
Bar code scanners have also been proposed wherein the outgoing laser beam is focused by different areas of the focusing lens such as described in U.S. Pat. No. 5,565,668 (Reddersen et al.). This design permits the beam to be focused to more than one waist location and, in theory, to provide increased depth of field. Because the light from the out-of-focus beam is still present when the other beam is in focus there is the potential for reduced resolution for each zone.